Answer: the solution 1.0 M Ca Br2.
This is becasue the freezing point depression is a colligative property.
A collegative property is one that depends on the number of particles in solution.
Each mole of KBr will produce two moles, one mole of potassium ion and one of bromine ion
Each mole of CaBr2 will produce three moles, one of calcion ion and two of bromine ion.
Then, the depression of the frezzing point will be greater in the case of the CaBr2, leading to a lower freesing point of the 1.0 M soluction.